The two acts of the play form a contrapuntal structure. Act 1 is set in British colonial Africa in the Victorian era, and Act 2 is set in a London park in 1979. However, between the acts only twenty-five years pass for the characters. Each actor plays one role in Act 1 and a different role in Act 2 - the characters who appear in both acts are played by different actors in the first and second. Act 1 parodies the conventional comedy genre and satirizes Victorian society and colonialism. Act 2 shows what could happen when the restrictions of both the genre of comedy and Victorian ideology are loosened in the more permissive 1970s.

The play uses controversial portrayals of sexuality and obscene language and establishes a parallel between colonial and sexual oppression.[2] Its humour depends on incongruity and the carnivalesque, and helps to convey Churchill's political message about accepting people who are different and not dominating them or forcing them into particular social roles.

Clive, A British colonial administrator, lives with his family, a governess and servant during turbulent times in Africa. The natives are rioting and Mrs Saunders, a widow, comes to them to seek safety. Her arrival is soon followed by Harry Bagley, an explorer. Clive makes passionate advances to Mrs Saunders, his wife Betty fancies Harry, who secretly has sex with the servant, Joshua, and Clive's son, Edward. The governess Ellen, who reveals herself to be a lesbian, is forced into marriage with Harry after his sexuality is discovered and condemned by Clive. Act 1 ends with the wedding celebrations; the final scene is Clive giving a speech while Joshua is pointing a gun at him.

Act II

Although Act 2 is set in 1979, some of the characters of Act 1 are reappearing – for them only 25 years have passed. Betty has left Clive, her daughter Victoria is now married to an overbearing Martin, and Edward has an openly gay relationship with Gerry. Victoria, upset and distant from Martin, starts a lesbian relationship with Lin. When Gerry leaves Edward, Edward, who discovers he is in fact bisexual, moves in with his sister and Lin. The three of them have a drunken ceremony in which they call up the Goddess, and after that characters from Act 1 begin appearing in Act 2. Act 2 has a looser structure than Act 1, and Churchill played around with the ordering of the scenes. The final scene shows that Victoria has left Martin for a ménage à trois with Edward and Lin, and they are sharing custody of their son Tommy. Gerry and Edward are on good terms again, and Betty becomes friends with Gerry, who tells her about Edward's sexuality.[2]

Act 1 of Cloud Nine invites the audience to engage with Britain's colonial past, but does so by challenging 'the preconceived notions held by the audience in terms of gender and sexuality'.[3] Churchill deliberately subverts gender and racial stereotypes, using cross-gender and cross-racial casting: Betty is played by a man in act 1, but by a woman in act 2, Joshua is played by a white and Edward is played by a woman in act 1 and by a man in act 2. Churchill deliberately uses the notion of cross gender, racial and age casting to unsettle the expectations of her audience. In the introduction of the play, Churchill explains why for example Betty is played by a man in the first act: "she wants to be what men want her to be ... Betty does not value herself as a woman." Michael Patterson confirms this when he writes that "Betty is played by a man in order to show how femininity is an artificial and imposed construct".[4] James Harding suggests that by cross-casting Betty and Edward in Act 1, Churchill is actually playing it safe: making what are same-sex relationships into ones that are visibly heterosexual and normative.[5]

The black servant, Joshua, is played by a white man for similar reasons. He says, "My skin is black, but o, my soul is white. I hate my tribe. My master is my light"; Amelia Howe Kritzer argues that he is played by a white man because "the reversal exposes the rupture in Joshua's identity caused by his internalization of colonial values".[6] Joshua does not identify with his "own" people; in act 1, scene three Mrs. Saunders asks if he doesn't mind beating his own people. Joshua replies that they are not his people, and refers to them as being bad.

Act II

The second act is set in London 1979, but for the characters only twenty-five years have passed. Churchill explains her reason for this in the introduction: "The first act, like the society it shows, is male dominated and firmly structured. In the second act, more energy comes from the women and the gays." In Act 2, the British colonial oppression is also present, this time in the form of the post-colonial presence in Northern Ireland. Although the different societies in the two acts are quite different, they share the notion of colonial oppression. Michael Patterson writes that "the actors ... established a 'parallel between colonial and sexual oppression,' showing how the British occupation of Africa in the nineteenth century and its post-colonial presence in Northern Ireland relate to the patriarchal values of society"[7] Churchill shows the audience different views of oppression, both colonial and sexual. She amplifies social constructs by linking the two periods, using an unnatural time gap. Amelia Howe Kritzer argues that "Churchill remained close to the Brechtian spirit of encouraging the audience to actively criticize institutions and ideologies they have previously taken for granted".[6]

There is a lot of difference between the two acts: Act 2 contains a lot more sexual freedom for women whereas in Act 1 the men dictate the relationships. Act 2 "focuses on changes in the structure of power and authority, as they affect sex and relationships" a male-dominated structure defined in the first act. Churchill writes that she "explored Genet's idea that colonial oppression and sexual oppression are similar."[6] She essentially uses the play as a social arena to explore "the Victorian origins of contemporary gender definitions and sexual attitudes, recent changes ... and some implications of these changes."[6]